THE RELATIONSHIP OF STRUCTURES AND AIR CONDITIONING TO INDOOR AIR QUALITY IN TWO INDOOR SWIMMING POOLS

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1 THE RELATIONSHIP OF STRUCTURES AND AIR CONDITIONING TO INDOOR AIR QUALITY IN TWO INDOOR SWIMMING POOLS T Jauhiainen 1, T Keskikuru 1, R Halonen 1, M Reiman 2, L Kujanpää 2, P Yli-Pirilä 1, T Raunemaa 1 and H Kokotti 1* 1 University of Kuopio, P.O.B 1627, FIN Kuopio 2 Institute of Occupational Health, P.O.B 93, FIN Kuopio ABSTRACT IAQ was studied in two indoor swimming pools located in the same city, an old one and a new one. Both the swimming pools had concrete constructions, but the new one had steel framework and wooden roof structure. The old one was equipped with an old HVAC system needing renovation and the new swimming and sport centre was equipped with an HVAC system of the latest technology. The ventilation system in the old building used short circuit airflow, which did not reach the swimmer. Velocities of airflows ( m/s in the old building and m/s in the new building) on the water level of the swimming pools were faster along the length of the swimming pool than across width of the pool. The airborne concentrations of microbes were fairly low, although the presence of microbes favouring moisture conditions is not acceptable, e.g. in the air of office buildings. INDEX TERMS Indoor swimming pool, Moisture problems, Construction and renovation, HVAC, Airborne microbes INTRODUCTION Among the most important factors in indoor swimming pools are air conditioning and air quality. Indoor swimming pool should be depressurised during every season to make structures invulnerable to potential moisture and microbial damage. Swimmers have been reported (Potts 1996) to complain of skin and eye irritation, throat pain, stuffy nose and in the more serious cases the respiratory allergy. The swimmer takes all the breathing air just above the water level. We studied indoor air factors in two indoor swimming pools located in the same city. The old swimming pool was built in 1968 and the new one in The aim of the study was to investigate the effectiveness of the air conditioning system, e.g. availability of fresh air at the water level, thermal conditions and building physics from the structural point of view. The concentration and diversity of airborne microbes were used as indicators of indoor air quality. MATERIALS AND METHODS In both the buildings, the main concrete constructions were quite similar. Because it was not possible to open the structures, the only methods to investigate the buildings were visual estimation and studying archival drawings. In the old indoor swimming pool, the measurement period was from to and in the new swimming centre from 3.5. to At the same time with continuous measurements of pressure difference (Setra 264 and Setra 267) between the indoor swimming * Contact author Helmi.Kokotti@uku.fi 842

2 pool and outdoors, we also measured the temperature and relative humidity (Vaisala RH/T HMP 143A and HMP 233A) in the supply air. The pressure difference in the indoor swimming pool was measured both at floor level and ceiling level. The measuring points were at the water level, in the incoming air, in the exhaust air, on the ceiling, and outdoors on the north side of the building. The amounts of airflow rates of the ventilation system were measured (Thermo anemometer Air Floe TA 5) in the ducts and in the air terminal devices. The amounts of supply air and exhaust air were determined by the airflow velocity in the ducts. The mechanical supply and exhaust flow rates (mechanical air- exchange rate) of air through main ducts were measured with devices of air velocity (TSI 8345). In the old indoor swimming pool, the direction of flow of the supply air was across the swimming pool. The terminal devices were about 6 metres over the water level. In the lengthwise direction the terminal devices were placed only on half the length of the swimming pool (Figure 1). In the new swimming centre the main terminal devices were under the ceiling, about 15 metres over the water level (Figure 3). The air velocity over the pool was measured 30 cm above water level and 100 cm from the edge of the pool. In addition in the old indoor swimming pool, air velocities were measured on the walkway beside the pool and in the stand for spectators. The airflow velocity was measured with a SwemaAir 30 -thermo anemometer (measuring error ± 6 %, minimum 0.05 m/sec). At every point the flow velocity was measured in the direction of the length and in direction of the width of the pool. The air temperature was also measured at some points with the thermo anemometer (minimum ± 0.5 C). Figure 1. HVAC system in the old indoor swimming pool Air samples were collected with an Andersen 6-stage cascade impactor using a volume flow rate of 28.3 litres/minute. Surface samples were swept with sterile swabs immersed in sterile 843

3 buffer. Material samples were analysed by direct plating method (Reiman et al. 1999). Microbes from different samples were cultivated on three different media: Rose Bengal-malt extract agar (Hagem) for fungi requiring high water activity, dichloran-glycerol-agar (DG-18) for fungi capable of growing in low water activity and tryptone-glucose-yeast-extract agar (TYG) for bacteria. After a week s incubation at + 25 C, the colonies were counted and identified using common mycological procedures. Results from air samples are expressed as cfu/m³ (cfu = colony forming unit) (Burge and Otten 1999). Figure 2. HVAC system in the new swimming centre. Structures The old indoor swimming pool had the barrel-shaped structure of pre-stressed concrete, but wall frames in the building were concrete. The indoor surfaces were covered with wooden materials having apparent signs of moisture damage. As a vapour barrier was a 0.2 mm thick plastic sheet, and 200 mm thick rock wool acted as thermal insulation. The load-bearing walls of the new swimming centre were concrete. In the walls, 180 mm thick rock wool was used as thermal insulation. As facade material there were sheet metal panels. The roof structure had the steel framework and the timber joist. There was no covering on indoor surfaces, except the cement particleboard in the ceiling. The thermal insulation was 250 mm thick rock wool, and lined plastic sheet acted as the vapour barrier. RESULTS The old indoor swimming pool Air conditioning One of the outdoor air grilles had had problems with freezing, snow and rainwater. The filtering of the outdoor air was not effective, and there were leaks in the filters. Whole the ventilation system was dusty and dirty. The exhaust fan of the old swimming pool was not working. The use of air conditioning had been limited during wintertime because of the 844

4 harmful decrease in temperature in the indoor swimming pool. The whole air conditioning system was not in accordance with present standards. In the beginning of the measuring period the old indoor swimming pool was depressurised, and during the second half of the measuring period, the pressure difference was balanced or fluctuated. The mean value for the pressure difference between the floor level indoors and the outdoor air was 3.8 Pa, and the mean pressure difference between ceiling and the outdoor air was 2.3 Pa. (Figure 3) The main part (62 %) of the exhaust air flow was conducted from the upper parts of the spectators stand and near the supply air devices in the old indoor swimming pool. The throw length of the terminal devices for incoming air was not adequate and it was not long enough to reach across the swimming pool. The rate of air change per hour in the indoor swimming pool was about 0.8. The air velocity above water level was lower than 0.05 m/s. The temperature of the incoming air was + 26 C and the temperature of the air in the basin room were higher being +30 C. Just above the water level the mean temperature was C ( C) and near the ceiling C ( C). The mean temperature of the supply air was C ( C). The temperature of the supply air was not utilized to adjust the indoor temperature. The relative humidity in the indoor swimming pool was not high, the mean value was 41 % RH (29 55 %RH), indicating that the amount of re-circulated air was minimal and amount of the fresh air and air drying caused by air change were maximal in the swimming hall. 4 Pressure difference (Pa Ceiling Floor Date Figure 3. The pressure differences (Pa) between indoor air and outdoor air monitored continuously as ten minutes averages at floor level and on the ceiling in the old indoor swimming pool during a week ( ). Microbes The concentrations of airborne fungi were lower than in outdoor air, however, ranging from 65 to 711 cfu/m 3. Single spores of Acremonium were found in supply air filter. Eight air samples out of ten included fungi favouring moisture environments (e.g. Acremonium, Aspergillus (A.) versicolor, A. penicillioides, A. ochraceus, Tritirachium, and Oidiodendron). Surface samples included some additional fungi (Aureobasidium, Scopulariopsis, Chaetomium, Rhizopus, Mucor, Paecilomyces, and Sphaeropsidales). Cladosporium, Penicillium and yeasts were common to air and surface samples. 845

5 The new swimming centre Air conditioning The location of supply air grille prevented the penetration of water and snow into the grilles. According to visual estimation, the surfaces inside the air treatment system were clean. To minimize contamination of the unit, there was a filter (EU5) in the exhaust air before the heat recovery unit. The supply air unit was equipped with pre-filter (EU5) and a fine filter (EU7). The indoor swimming pool was extremely depressurised. The mean difference between the pressures at floor level and outdoors was greater than 20.0 Pa, and the mean difference between the pressures in the ceiling and outdoors was greater than 16.3 Pa (Figure 4). 5 Ceilin g Pressure difference (Pa Floor Date Figure 4. The pressure differences (Pa) between indoor air and outdoor air monitored continuously as ten minutes averages at floor level and on the ceiling in the new swimming centre during In the air dryer engine the airflow was 3 m³/s and in the fresh air fan the airflow was 5 m 3 /s. The amount of fresh air was 37 % of the total amount of supply airflow. The air change rate calculated from supply air rate was 0.36 times per hour. However, the actual air change, including the amount of leakage air, was lager. The total rate of air change in the indoor swimming pool, including the leaks caused by the negative pressure in the indoor swimming pool, was about 0.5. The air change was not even throughout the whole indoor swimming pool, and the air velocity above the water level of the pool was very low ( m/s). The temperature of the supply air from the air dehumidifier was warmer (+40 C) than the air on the water level of the pool ( C), which was the same as the temperature of fresh air in the upper part of the indoor swimming pool. Above the pool level the mean temperature was C ( C) and near the ceiling C ( C). The average value of the water content of the supply air was much higher than one of outdoor air, which revealed that supply air consisted mostly of re-circulated air. This was caused by the air conditioning system utilizing only re-circulated air as supply air and exhaust fans during nights. The moisture in the air was not removed by the air conditioning. On the other hand, at night the production of humidity was minimal, and so the water content in the indoor air was lower than in daytime. 846

6 Microbes The concentrations of airborne fungi were remarkably lower than in outdoor air, ranging from 6 to 54 cfu/m 3. All air samples (8/8) included fungi favouring moisture environments (e.g. Aureobasidium, Aspergillus (A.) versicolor, A. fumigatus, A. penicillioides, Eurotium, Fusarium, Tritirachium, Oidiodendron, and Wallemia). Surface samples included some additional fungi (A. versicolor, Ulocladium and Sphaeropsidales). Cladosporium, Penicillium and yeasts were common to air and surface samples. DISCUSSION According to our results it is very difficult to have a good air conditioning in an indoor swimming pool. In the old one there were problems with the old-fashioned system, which kept the rate of air change poor, and the air velocity above the swimming pool very low. The control and adjustment unit for the heating, ventilation and air conditioning (HVAC) system in the new swimming centre was adjusted by the temperature, relative humidity and carbondioxide concentration measured in indoor air. However, this system cannot guarantee good IAQ for the swimmers, because the air distribution network does not take account the special problems due to a pool. This may explain the symptoms swimmers complain generally, because they take all the air for breathing from just above the water level. In the old building the most of the indoor surfaces were covered with wooden materials, which were observed to be damaged by moisture. Concentrations of airborne fungi in this building were ten fold higher than in the new swimming centre, where the indoor surfaces of concrete constructions were painted and showed no signs of damages. Great variety of fungi favouring moisture environments were found in both the buildings. Similar findings have been made in one case study earlier (Jauhiainen, et al. 2000). This might probably indicate indoor climatic conditions keeping even delicate microbes viable and encourage their growth in poorventilated areas. In our case, microbes could have originally been come from moisturedamaged structures or outdoor air. ACKNOWLEDGEMENTS Finnish Ministry of Education founded this study. REFERENCES Burge HA, and Otten JA Fungi. In Bioaerosols: Assessment and Control, Macher JM, ed. Cincinnati OH: ACGIH, pp Jauhiainen T, Reiman M, Lindberg R, et al The significance of a vapour barrier in the roof structure of an indoor swimming pool, Proceedings of Healthy Buildings 2000, Vol. 3, pp Espoo: Healthy Buildings Pots J. Factors associated with respiratory problems in swimmers Sports Med 21 (4) Reiman M, Haatainen S, Kallunki H, et al The characteristics of the dilution and direct plating methods for the determination of microbial flora and concentrations in building materials, Proceedings of the 8 th International Conference on Indoor Air Quality and Climate - Indoor Air '99, Vol. 4, pp Edinburgh: Indoor Air '